1. Field of the Invention
The present invention relates to printing operations. More specifically, the present invention relates to printing systems that employ movable print heads and process a variety of print jobs.
2. Description of the Related Art
High volume printing and mailing operations face a variety of challenges that are not present in low volume and manually operated printing and mailing operations. In a high volume operation, there are frequently large numbers of media pages or mail pieces that are of a consistent size and that are processed in a single print job with only slight variations, such as differing addresses. In a typical high volume printing operation, a large number of different jobs may be processed from time to time and the printed media and mail pieces may vary from job to job.
Handling large volumes of printed items and mail pieces and printing variable addresses on the mail pieces requires high-speed equipment. While a simple office laser or inkjet printer may suffice for printing envelopes in a small mail-volume office, in a high-volume operation, specialized machines are used for printing addresses, return addresses and other variable text and images onto media pages and mail pieces.
One approach is to use a printing machine with two or more print heads that are moveable along parallel axes and to set each print head at a fixed position along its axis, where it remains for the duration of each job. For example, a first print head may be positioned to print a delivery address near the middle of an envelope and a second print head positioned to print a return address near the top of an envelope. The print heads need not be moved along their respective axes unless the media size or printing positions change. During the printing operation, the media to be imprinted is moved laterally with respect to the print head axes as the print heads imprint characters or images onto the media. This approach is used with high-speed ink-jet printers, but the same approach also applies to offset printers, dot-matrix printers, and other print head technologies.
In an inkjet print head, when implemented in a fixed head configuration, each print head comprises a row of nozzles that spray ink droplets onto the media as it passes in front of the printing head. The modulation of the nozzle spray droplets, synchronized with the movement of the media, enables the formation of characters and images in the ink droplet spray patterns.
The positions of the print heads are changed when the media size changes or when the printing positions on a given media size are changed. In prior systems, it is common for the print head position to be changed manually by sliding the print head up or down its axis, and then securing it in a fixed position with a set screw. In operation, a technician determines the required vertical offset for each print head position according to the print job specifications and then measures or otherwise calibrates the print heads along their vertical mounting axes at positions consistent with the job's printing requirements. The print head position determines the vertical position of the print on the media. The printing positioning along the lateral dimension of the media is determined by the timing relationship between the start of the print operation with respect to the lateral starting position of the media under the print head. In the prior art, the lateral positioning task is automated and under the control of a printing controller. The task of changing print head positions necessarily shuts down the printing and processing functions.
It is desirable to minimize down time in a high volume printing or mailing operation, and it is common for a processing line to run nearly continuously during a work shift. While many printing jobs involve the printing of a large number of similar items, modern processing machinery operate at very high speeds. Consequently, the print head positions may be changed frequently during a typical shift. Changing print head positions consumes time, increases wear and tear on equipment, and results in reduced efficiency of a processing operation. Even in systems that employ automated print head position changes, each change produces the aforementioned undesirable results.
Thus there is a need in the art for a system and method for reducing the frequency with which print head positions must be changed in a printing or mailing operation.